GB-A-2183672 discloses a process to prepare a Fischer-Tropsch synthesis product starting from natural gas. In this process carbon dioxide is removed from the syngas as prepared in a reformer step and recycled to be used in said reformer step.
WO-A-9603345 describes a process to prepare a mixture of carbon monoxide and hydrogen by partial oxidation of natural gas in a co-annular burner using 99.5% pure oxygen and optionally carbon dioxide as moderator gas and in the absence of a catalyst. The temperature of the natural gas feedstock is between 150 and 250° C. in one example and between 280 and 320° C. in another example. The reactor temperature in the examples is between 1250 and 1400° C.
A disadvantage of the above process is that the consumption of oxygen is high.
WO-A-03/000627 describes a process to prepare a Fischer-Tropsch synthesis product from a gaseous mixture of hydrocarbons comprising methane, ethane and higher carbon number hydrocarbons. The process steps comprise a reforming step performed on the hydrocarbon mixture in the presence of a reforming catalyst, wherein the heat for performing this reaction is supplied by indirect heat exchange with a hot gas. The hot gas is the effluent of a partial oxidation of the effluent of the reforming step and a CO2 depleted off-gas of a Fischer-Tropsch process as performed further downstream of these processes. A disadvantage of such a heat-exchange step is that it requires a complicated reforming reactor.
WO-A-2004/096952 describes a process to prepare a Fischer-Tropsch synthesis product from natural gas by passing a mixture of Fischer-Tropsch off-gas and natural gas over an adiabatically operated pre-reformer reactor. The effluent is subsequently used as feed in an auto-thermal reformer (ATR) reactor. The synthesis gas as obtained is used as feed to a Fischer-Tropsch step. The Fischer-Tropsch off-gas may also be added to the feed of the ATR reactor. In order to avoid decomposition of the hydrocarbons in the Fischer-Tropsch off-gas it is preferred to avoid heating this stream to temperatures above 420° C. prior to combining this stream with the feed of the ATR reactor. According to this publication it is preferred to add Fischer-Tropsch off-gas containing hydrocarbons other than methane to the feed of the pre-reformer reactor in order to avoid carbon deposition in the ATR reactor.
The present process involves an improved process to prepare a Fischer-Tropsch product wherein the consumption of oxygen is reduced.